Process and apparatus for screening materials



PROCESS AND APPARATUS FOR SCREENIISQ IATERIALS Filed Sept. 29. 1926 2 Sheets-Sheet 1 mu 51: :23% w 0,, g: l E 2. E f: if :5: a i 0% J MM,

z i A t i z April 23, 1929.

, L. s. DEITZ, JR

no'csss AND APPARATUS FOR SCREENIJG nu-nuns "2 Sheets- 811001.

Filed Sept. 29. 1926 Patented Apr. 23, 1929.

LOUIS S. DEITZ, JR., RIFLE, COLORADO.

PROCESS AND APPARATUS FOR SCREENING MATERIALS.

Application filed September 29, 1926.

The present invention relates to a process and apparatus for screening or classifying materials and the object is to provide a process for this purpose and an apparatus of this character which will ellectively screen out evenly, with substantial completeness and expedition, the finer gradesthat is to saythe smaller sized particles of vconnninuted sub stances. I

In the accompanying drawings Figure 1 is a diagrammatic view in plan of one embodiment of the apparatus,

Figure 2 is a plan View of a different form of construction,

Figure 3 is a sectional View on the line 3-3 of Figure 2. e c

F igure 4 is a plan view of another embodiment of the invention in which a rotary screen is employed.

Figure 5 is a detail View on a magnified scale indicating the operation that takes place.

In the present process the solids made up of relatively large and small particles are mixed with water or other liquid and are held in suspension therein. This liquid is then caused to flow in a slow moving stream. Extending through and across the stream is a screen. This screen is caused to have a movement transversely to the direction of movement of the stream and at a speed decidedly in excess of the speed of the stream. It has been found that for each condition there is a definite ratio of speed of screen to speed of solution, above which the screen will operate and below which it will instantly clog.

It has been found that with such a combination and action, a relatively coarse screen can be employed and yet only particles of much less area than the area of the screen openings will pass through the screen, while particles of approximately the size of the screen openings and indeed those materially less than the same will not pass through the screen but will be held back and will either drop to the bottom whereby they may be extracted or can be otherwise disposed of.

By this operation, greater screening rates and denser pulps can be used while a highgrade classification is secured.

The apparatus for carrying out the process may be embodied in various forms. Thus referring to Figure 1, a tank or container 6 is employed having a relatively large body and an intake teed portion 7 of less cross sectional suitable Serial No. 138,520.

area than the body 6. The outlet end is indicated generally at 8 and may lead to any rece1ver. The liquid that constitutes the veh cle for the materials to be separated or class fied and carrying such materials in suspension, is delivered from any suitable source to the feed inlet 7 and flows in the direction of arrows into the body 6 where it spreads out into a large mass that has a slow movement through said body to the outlet end 8. In the body and extending through and across the stream is a screen indicated at 9. This screen is movable edgewise and is operated by any suitable means through and across the stream of material. For example, it may be vibrated either horizontally or vertically. Its movement, except when it comes to rest at the ends of its stroke, is at a greater rate of speed than the movement of the material bearing liquid. It has been found that by reason of this relatively rapid movement of the screen only fine particles much less in area than the area of the screen openings are allowed to pass, while the larger particles, even of considerably less size than the screen openings and those approximately the same size will not pass through the screen but will be bafiled back. It has been found, moreover, that with such a structure the screen is not apt to become clogged.

A practical embodiment of the invention is illustrated in Figures 2 and 3. In this form of structure a cylindrical casing or container 10 is employed having a feed trough 11 surrounding its upper portion with ports 12 opening from the trough to the interior of the container at various points. An outlet for the fine material is shown in the form of a vertical centrally disposed pipe'13 having a coupling 14 at its lower end that connects with an outlet pipe 15. The pipe 13 is provided with inlet ports 16. The bottom of the container lO may have an outlet 17 for the residues. The outlets 15 and 17 may be provided with suitable controlling valves 18 and 19. Mounted on the vertical pipe 13 and surrounding the portion of the same having the inlet ports 16 is atubular screen 20 through which the liquid entering the container, must pass in order to gain access to the ports 16 and thus to the interior of the pipe 13. The

. lated.

The liquid carrying in suspension the materials to be separated, enters through the ports 7 12 from the trough l1 and has a slow move- 'ment inwardly to the pipe 18, the rate of flow being, of course, controlled by thevalve 18. This pipe and screen are caused to oscillate and the rate of speed of the screen is made materially greater than the rate of flow of the liquid to the pipe. The consequence is that only fine particles of materially less area than thescr'ee-n openings will pass through the screen and flow out with the liquid through the pipe 15. The larger materials being baflled back, finally escape with a portion of the liquid through the outlet 17.

Instead of an oscillatory or reciprocatory screen, a rotary screen may be employed and would theoretically appear to be most satisfactory. Inasmuch, however, as experience has demonstrated that the particles should approach the screen at substantially right angles to the screens surface, the friction between the liquid and the screen has a tendency to cause the liquid and consequently the particles to move with the screen. "With a reciprocating or oscillating screen this tendency is substantially neutralized but with a continuously rotating screen the movement of the liquid with the screen is increased. Battles, however, may be employed to prevent the formation of currents that thus move with the screen. In Figure 4, an outer cylindrical casing is shown at 23 with a cylindrical screen 24, rotatively mounted therein, the outlet for the liquid carrying the fineparticles being illustrated at 25. The screen may be given a continuous rotation in one direction as, for example, in the direction shown by the arrow. Interposed between the casing 23 and screen 24 are inwardly extending baffies 26 that terminate just short of the screen and thus have a tendency to prevent a circular motion of the liquid with the screen.

The probable action that take place will be clear by reference to Figure 5 wherein a portion of a screen is shown greatly magnified, the solid elements thereof being designated 27 and the spaces between them or the screen openings being shown at 28. A large particle is shown at 29 and a smaller particle at 30. These particles move in the direction shown by the arrow 31 and the screen has a movement transverse to the direction ofmovement of the particles as will be evident. With this structure the smaller particle 30 is shown as passing through one of the openings and will proceed far enough before the adjacent bar or solid portion 27 engages it so that it will pass on through the right hand side of the screen. The area of the larger particle 29 being greater and the space between the adjacent bars 27 being reduced by the movement of the screen the chance of the particle 29 passing the screen is greatly reduced. other words, it will be struck by one ofthe bars 27 and baffled back. Inasmuch as the slow movement of the liquid will carry it forwardly at a low rate of speed it is almost bound to be again struck and' consequently it gradually sinks to the bottom and below the screen without passing the same. It will be understood that this invention is intended primarily for fine materials and in which fine mesh screens are employed. It has been found, however, that for the same work of line screening, a coarser and therefore strongor screen can be used, due to the baffling action previously described than has been possible with the ordinary methods. Also for the same reason the rate of material screened is greatly in excess of that obtained by old methods. And a further advantage results in the fact that the screens are not apt to clog.

After careful tests, it has been found that with screens of 60 mesh having openings of about 35% of the screen area the maximum speed of a liquid approaching the screen and carrying from 20% to 50% solids is about 1.5 feet per minute. Above this rate of speed of the liquid, the screen will clog. It is of course slower for finer screens. Using a 60 mesh screen with a .0085 inch opening, the percentage of 60 plus 100,, mesh product passing through the screen is about 2%, thus indicating the efiicicncy of the machine. This efficiency is not alfected appreciably by the percentage of solids in the pulp except with great dilution. Nor is it affected appreciably by the rate at which the solution passes through the screen. There is, however, a little less than 60 plus mesh product as the rate decreases. It is also found that the efliciency is not affected appreciably by a change in the number of vibrations of the screen per minute for the same length of stroke of the screen, if within limits of 40 and 200 vibrations per minute, though the screen has more. of a tendency to clog with the slower rate of vibration. Indeed, it has been found that the screen will clog with a rate lower than 40 vi brations per minute where the screen is of 60 mesh and there is 35% solids in the pulp. It has also been found that the efliciency is affected by any movement or agitation of the pulp on the feed side of the screen and that the p thus allow some of the coarser particles to pass through.

The following table is a result of careful tests made Screen cloth, 60 mesh. Rate of oibra-tion,constant at 150 per minute.

Size of feed stroke 1" stroke 3' stroke Density of feed. solids.

Density of discharge through screen, 18% solids.

Rate of screening 3.76 grins. solids per sec, per sq. in. of screen cloth.

With the same screen and conditions as in the above tests, using a one inch stroke and varying only the. number of strokes per minute with a view to showing the limits of cloggm g, the following results were obtained:

Size of product passing through screen.

Strokes per min.

Size of feed 0. 0% 0. 0% 0. 0% 0.0 o. o 0.0 2. o 1. e 2.1 11.5 10. s 11. 4 86. 5 87. e 80. 5

ous tests, also 35% solids. Size of material passing through screcn.

Rotation speed of screen surface feed so R. P. M 113 R. P. M. 200 R. P. M. 39 ftJmin 89 ItJmin. 157 (tr/min.

The above shows that the screened product with the use of a rotary screen is much coarser, due to the agitation of the solution adjaent to the feed side of the screen. It was also found that the capacity before the clogging point was not as high as with a vibrating screen.

From the above it seems demonstrated that three features are important 1. Rate of movement of screen surface.

2. Rate of movement of pulp liquor approaching the screen.

3. Direction of motion of pulp liquor approaching the screen.

From the foregoing it is thought that the construction, operation and many advantages of the herein described invention will be apparent to those skilled in the art, without further description, and it will be understood that various changes in the size, shape, proportion and minor details of construction and operation may be resorted to without departing from the spirit or sacrificing any of the advantages of the invention.

What I claim is 1. The method of separating materials which consists in creating a flowing stream of said materials, causing said stream to flow through a screen at right angles to the screen, moving said screen transversely to the stream. and preventing the formation of material transverse movement of the stream adjacent to the receiving side of the screen.

2. The method of separating materials which consists in creating a flowing stream of said materials, causing said stream to flow through a screen at right angles .to the screen, moving said screen transversely to the stream at a sufiiciently greater rate of speed than the rate of speed of the stream to battle back away from the screen and against the stream, the coarser materials, and preventing material. agitation and cross current in the stream adjacent to the receivii'ig side of the screen.

3. In an apparatus of the character set forth, a container having an inlet for a liquid having the materials to be classified in suspension therein, an outlet for the liquid and one grade of classified material, a screen movably mounted in the container between the inlet and the outlet, means for causing the liquid to flow through the screen at a predetermined rate, means for causing the screen to move through the liquid transverse to its direction of movement and at a greater rate of speed than the speed of the liquid, and means adjacent to the screen for preventing cross currents in the flowing stream adjacent to the upstream side thereof.

4. In an apparatus of the character set forth, a container having an inlet for a liquid having the materials to be classified in sus pension therein, an outlet for the liquid and one rade of classified material, a screen mova 1y mounted in the container between the inlet and the outlet, means for causing the liquid to flow through the screen at a predetermined rate, means for vibrating the screen through the liquid transversely of its direction of flow and at a speed greater than the speed of the liquid, and bafilcs on the upstream side of the screen and adjacent thereto for preventing material currents crosswise to the stream and longitudinally of its directron of movement.

- a fluid with the materials to be classified therein, to the container on one side of the screen, means for carrying ofl the fluid from the other side of the-screen, means for controlling the rate of flow of the fluid through the container, means for rotating the screen, and bafilesmounted in the container on the upstream side of the 'screen and directly adjacent thereto to prevent the creation of cross currents at the screen that would otherwise be created thereby.

6. The method of separating materials which consists in creating a quietly flowing stream of said materials, causing said stream to flow through a screen placed across the same, and me ing said screen transversely to the stream at a speed sufiiciently greater than the speed of the stream to cause the coarser materials to oe struck and battled back away from the screen against the flowing screen, the screen being thereby kept substantially unobstructed by its own action in the stream, and maintaining a constant and substantially undisturbed flow of the stream adjacent to and throughthe screen.

In testimony whereof, I afiix my signature.

LOUIS S. DEITZ, JR. 

